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Topic Title: horses electric fence, earth rods
Topic Summary: distance between horse earth rod and domestic earth rod
Created On: 11 November 2012 09:13 PM
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 11 November 2012 09:13 PM
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loftyloo

Posts: 588
Joined: 23 May 2006

hi, has anyone got any information regarding the safe distance the earth rods should be apart so not to affect the mains distribution system ?
any information would be helpful,


thanks


lofty
 11 November 2012 09:24 PM
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slittle

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I'd go at least several times the length of the rod.

To be honest I doubt very much the fence would effect the mains side (in fact I know it normally doesnt) but I'd be slightly concerned about an earth fault on the mains installation possibly lifting the "earthy" side of the fence controller up.

If you take it to it's worse case with a shared rod (which I've seen done) and a faulty RCD, you could have a few "mains" volts hanging around on the fence as well as the 6KV from the fence controller.


Stu
 11 November 2012 09:36 PM
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loftyloo

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Thanks for the reply, I think I'm looking at about 15 Mtrs away, never fitted a main electric fence before


Lofty
 11 November 2012 09:40 PM
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slittle

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Two bits of advice then,

1) don't touch it
2) don't try and measure it



Stu
 11 November 2012 10:38 PM
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stateit

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Originally posted by: slittle

Two bits of advice then,



1) don't touch it

2) don't try and measure it


Stu


You can get a tester for not many pounds which you can factor into the price for the job - will let you know where there may be any faults.

I peed on one accidentally (fence, not tester) as a kid while night fishing (peeing in a hedge - thought it a reasonable thing to do). They blooming well hurt.

-------------------------
S George
http://www.sg-electrical.com
 11 November 2012 10:43 PM
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John Peckham

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I saw a person try to hold down an electric fence with a rifle barrel while another was going to step over it which was very entertaining. Boots DMS black not that good an insulator then?

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John Peckham

http://www.astutetechnicalservices.co.uk/
 11 November 2012 10:53 PM
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stateit

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Wet footwear, even if wellies, are not that good an insulator. And they'd have been wet well before I was having a pee as well !

Certainly would not have wanted to know about it if barefoot!

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S George
http://www.sg-electrical.com
 11 November 2012 11:25 PM
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KFH

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As suggested get one of the little testers, just remember to put one end in the ground FIRST otherwise it can be painful especially with a mains powered unit. There is a minimum distance but I think it is something like twice the length of the rods, I did find it somewhere once, it may have been as much as 30ft. I did have one very close to the main earth and suggested to customer he move it. He then touched the end of the rod when moving some stuff around it and got a good belt, I suggested that perhaps it was not a very good earth anyway so he had the opportunity to make it work properly

I reached across an electric fence to stroke a horse, unfortunately my coat was touching an electric fence and I had good insulating boots on, the horse didn't so we both got a shock. It was a long time before she would come near me again :-(
 11 November 2012 11:49 PM
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alancapon

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Many years ago, it was seen as "entertainment" trying to connect friends bicycles to stock fences. We discovered that a longish blade of grass was good for testing a fence. You held one end, placed the other end on the fence, and by moving your hand closer to the fence, you could find a point where sufficient current flowed to make your hand flinch everytime the pulse came, but not enough to hurt.

Regards,

Alan.
 12 November 2012 08:33 PM
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weirdbeard

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Hi Lofty, there was a bit of info in the 16th Edition, Section 605-14-04 "Every earth electrode which is connected to the earthing terminal of an electric fence controller shall be be separate from the earthing system of any other circuit.and shall be situated outside the resistance area of any electrode used for protective earthing."
 13 November 2012 09:56 PM
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slittle

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I should have said "don't try and measure it with a normal meter"

Another good trick if you get involved moving any of the fence is to make sure you earth it down a few yards before where you want to touch it. Several times I've moved fences and some kind person has switched it back on whilst it was in my hand !


Stu
 13 November 2012 10:07 PM
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loftyloo

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guess thats what you call "horse play " lol



lofty
 14 November 2012 03:24 PM
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gordon.s1

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Well folks I can tell you it does affect mains earth !.
Just came back from a job where the security stuff had failed due to lack of power on the farm building !.
When checking found 30ma RCD was dead, after some hunting around found feed from another farm building also with a 30ma RCD !.
YES, I know not good so I will fix that problem later.
Anyway this kept tripping, so next time waited a while and could hear this clicking noise.
Followed sound to other side of large barn and there was this fencer with the ground alligator clip attached to the steel girder work,
As you can guess the girder work also was connected to mains earth, all bonded.
So with removal of fencer ground RCD stayed energized.
Now for the rest of problems.

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 14 November 2012 03:35 PM
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AJJewsbury

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So with removal of fencer ground RCD stayed energized.

Interesting - any thoughts on whether it was due to the fence controller "elevating" the local earth, or perhaps due to electro-magnetic interference? (like JP's walky-talkies)
- Andy.
 14 November 2012 03:53 PM
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gordon.s1

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I would think as it was a mains fencer it gives quite a wallop, lots of Joules.
This then travels through the metalwork to the earth connection of RCD !.
Hey Presto and POP goes the RCD.

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 14 November 2012 11:30 PM
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sparkyaj

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I posted a reply earlier on but it appears not to be here. I have seen rcd's taken out numerous times on farms becuase of electric fences pegged into the ground within the earth electrode area on TT systems.

This subject opens up like a can of works, but in short - here goes:

TT system through RCD feeds socket outlet = plugged into that is electric fence, Fence is plugged down to earth and fires as much as 300mAs.

If that fault current gets back via the earth electrode to its start point the RCD will trip. And trust me they do!

Take a 1mtr earth electrode - it will 'roughly' have a 1mtr radius out from its driven down location. Assume you have one rod in the ground and say 900mm away you have a fence into the ground. - the two 1mtr radius areas over lap allowing fault current to transfer back to the installation electrode and trip RCD.

So lets assume you have a good TT system earthing and have say 3 or 4 rods down - that radius becomes 3 or 4 mtrs. if the fence is down within this radius again you see the same problem.

Now lets assume you only have 1 mtr down but the earthing is poor, ground is damp - the 1 mtr radius could become 2/3 meters or until it finds natural earth.

Just for good measure - the next issue you can experience is extreamly high touch voltage on the ground between these two field loops. 2 rods installed 2 mtrs down would need a 2mtr gap between them. if the gap was actually more - 3mtrs you would think that is good.

BUT - when livestock stand between the two points - they become the path conductor - and you end up with a very expensive vet bill.

This really is an outline and as you will notice, so many factors can be changed. As a rule - I always ask my customers to use the fences as far away fro the house as they can - or use a battery powered device only. Hope that helps a little.
 15 November 2012 09:55 AM
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AJJewsbury

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If that fault current gets back via the earth electrode to its start point the RCD will trip. And trust me they do!

I don't doubt you! I was just wondering about the mechanism of it all - better understanding and all that...

I've thought up three possibilities so far (possibly none of which are correct):
1. EMI from the electric fence system inducing currents in the RCD's coils (in which case we might expect trips if the controller or fence was close to the RCD, regardless of the fence's rod location) - some shielding might help in that case.
2. The proximity of the fence's earth rod raises the electrical system's earth - RCDs with a white earth lead see this as a high potential between N and PE or low potential between L and PE, are fooled into thinking N has gone missing and trip as a safety precaution. Selecting a different type of RCD might avoid the problem.
3. The proximity of the fence's earth rod raises the electrical system's earth - coupled with an existing N-PE fault or leakage path - some of the Fence's current finds its way to earth via the installation N and supplier's N-earth link - thus throwing the RCD out of balance. Improving the installation's insulation values might help in this case.

Of course moving the fence/rod further away is the ideal, but it's not always practical, so other ideas might be useful.

- Andy.
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